The present invention relates to a gland packing which is to be used in a shaft seal portion of a fluid apparatus or the like.
Conventionally, as plural braiding yarns in a braided gland packing, for example, known are braiding yarns which are disclosed in, for example, Japanese Patent Publication No. 6-27546 and Japanese Patent Application Laying-Open No. 6-74346. In each of the braiding yarns, an expanded graphite tape is bent so as to contract in the width direction, the whole outer periphery of the bent expanded graphite tape is covered by a reinforcing member configured by a knitted body or a braided body.
An expanded graphite tape is easily affected by tension or torsion. In a braiding yarn of a gland packing, therefore, cracks (breaks) sometimes unwillingly occur in end portions in the width direction of an expanded graphite tape. As such cracks are larger in number and in size, and as the number of braiding yarns in which such cracks occur is larger, the sealing performance of the gland packing is further impaired.
Even in the case where such cracks do not exist immediately after the production of a gland packing, cracks sometimes occur when, after the production, the gland packing is compression-molded to a predetermined size or into an annular shape. In the case where a gland packing is set to an apparatus so as to function as a seal, when a large fastening force is applied to the packing, such cracks may occur. When such cracks occur immediately after the production of a gland packing, a situation that the cracks are expanded by the compression molding or the fastening force is of course caused.
The gland packing of the invention is configured so that, in a plurality of braiding yarns in a braided gland packing or a twisted gland packing, the braiding yarns include braiding yarns in each of which an expanded graphite tape is bent to contract in a width direction, and both end portions in the width direction of the bent expanded graphite tape are folded back.
The gland packing of the invention is configured so that, in a plurality of braiding yarns in a braided gland packing or a twisted gland packing, the braiding yarns include braiding yarns in each of which an expanded graphite tape is bent to contract in a width direction, and both end portions in the width direction of the bent expanded graphite tape are folded back.
According to the thus configured gland packing, the braiding yarns in a gland packing include braiding yarns in each of which an expanded graphite tape is bent to contract in a width direction, and both end portions in the width direction of the expanded graphite tape are folded back. Even when a crack occurs in an end portion in the width direction of the expanded graphite tape, therefore, either of the following states arises. In the case where the crack is large, there arises a state where the crack is broken to contract, and, in the case where the crack is small, there arises another state where the crack is opposed to an outer side piece portion of the bent expanded graphite tape. Therefore, the crack is not exposed in a state where the crack is straightly elongated as it is, so that impairment of the sealing performance of the gland packing can be suppressed.
In some cases, a gland packing is compression-molded to a predetermined size or into an annular shape after the production, or in the case where a gland packing is set to an apparatus so as to function as a seal, the gland packing receives a large fastening force. Also in such cases, when a gland packing comprises such braiding yarns, cracks hardly occur because the end portions in the width direction of an expanded graphite tape are folded back, and, when cracks already occur, it is possible to suppress expansion of the cracks.
As the number of such braiding yarns in a gland packing is larger, cracks in an end portion in the width direction of the expanded graphite tape exert less influence, and impairment of the sealing performance of the gland packing due to the cracks can be suppressed more effectively.
The other gland packing of the invention is configured so that, in a plurality of braiding yarns in a braided gland packing or a twisted gland packing, the braiding yarns include braiding yarns in each of which an expanded graphite tape is twisted, and at least an outer end portion in a width direction of the twisted expanded graphite tape is folded back.
According to the thus configured gland packing, the plural braiding yarns include braiding yarns in each of which at least an outer end portion in the width direction of a twisted expanded graphite tape is folded back. In the same manner as the gland packing having the above-mentioned configuration, even when a crack occurs in an outer end portion in the width direction of the expanded graphite tape, therefore, either of the following states arise. In the case where the crack is large, there arises a state where the crack is broken to contract, and, in the case where the crack is small, there arises another state where the crack is opposed to an outer side piece portion of the expanded graphite tape. Therefore, impairment of the sealing performance of the gland packing can be suppressed. The invention has another advantage that, even after the production, cracks hardly occurs in the outer end portion in the width direction of the expanded graphite tape in the same manner as the gland packing having the above-mentioned configuration. As the number of such braiding yarns in a gland packing is larger, impairment of the sealing performance of the gland packing due to cracks in the outer end portion of the expanded graphite tape can be suppressed more effectively.